If they ever were to make a move against Japan, I would expect it to most likely be in conjunction with China.
Then it may not seem so inplausible, if part of the Japanese strength, especially the majority of its AF and Navy gets drawn away south (?)
Russia may be far away to land army units, but not as far as Chinese would have to travel. So the plan may be
Airforce gets drawn south by Chinese air units.
Combined Russo-Chinese naval force to pin the JMSDF
Land operation by russians up north.
Why would they make a move against japan? they dont have motives for that. It would also drawn US into the fight. Thats something that they dont want to. IF anything, it is japan who might make a move againt russia, taking into account the huge disparity of conventional militar might betwen the two.
AFAIK chinese warplanes cant reach japanese main islands (except perhabs outdated H-6, easy prey for japanese air force). Chinese navy is weak against japanese navy, even in combination with russian navy.
I dont think what you propose is possible.